System and method for controlling electrodeposition coating

ABSTRACT

An exemplary system for controlling electrodeposition coating for electrochemically forming a coating film on a coating object in an electrodeposition tank storing electrodeposition solution includes, a positive electrode configured to apply a positive electrode voltage to a positive electrode disposed in the electrodeposition tank, a negative electrode configured to apply a negative electrode voltage to the coating object transferred by a hanger, and an electrodeposition controller configured to electrochemically deposit the coating film on an external surface and an internal surface of the coating object by applying the positive electrode voltage to the positive electrode and the negative electrode voltage to the negative electrode, where the electrodeposition controller may be configured to control voltage, current, and pulse in multi-stages over time from a dip-in time point to a draw-out time point of the coating object into and from the electrodeposition tank.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0155135 filed in the Korean Intellectual Property Office on Nov. 19, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Field

The present disclosure relates to a system and method for controlling electrodeposition coating.

(b) Description of the Related Art

In general, in the electrodeposition process of a vehicle production factory, the electrodeposition work of forming a coating film on a coating object such as a vehicle body is performed to prevent corrode of the vehicle body, and to improve sound insulation, rust prevention, and appearance quality.

In the electrodeposition work, a coating film is formed on the surface of the coating object through electrophoresis and electrolysis in the electrodeposition solution contained in the electrodeposition tank, and the thickness of electrodeposition film is controlled by controlling an applied voltage.

For example, FIG. 10 shows a scheme for the conventional electrodeposition.

Referring to FIG. 10, a coating object 10 is put into the electrodeposition solution contained in the electrodeposition tank, and a negative electrode (−) connected to the coating object and a positive electrode (+) provided in the coating are energized to electrochemically form a coating film. At this time, the higher the voltage is, the higher the coating film thickness is. Therefore, the electrodeposition film thickness is controlled by controlling the voltage of the rectifier connected to the electrode.

However, in the conventional voltage control method for electrodeposition coating, defects such as dipping marks may occur due to application of high current at the time of dip-in of the vehicle into the electrodeposition tank to complete the electrodeposition work within a short cycle time.

In addition, in order to secure the coating performance of the coating object, the thickness of the coating film of the external plate and the internal plate must satisfy a standard specification (for example, 11 μm or more).

However, conventionally, the current level of the internal plate is lower than that of the external plate, which causes a difference in coating film formation speed. Therefore, the amount of paint used is increased to form the coating film thickness of the internal plate to the standard, since the difference in coating film thickness between the external plate and the internal plate is high (for example, 5 μm or more).

The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY

The present disclosure has been made in an effort to provide a system and method for controlling electrodeposition coating that may reduce a coating film thickness difference between external and internal plates in electrodeposition coating.

An exemplary system is for controlling electrodeposition coating for electrochemically forming a coating film on a coating object in an electrodeposition tank storing electrodeposition solution, and the system includes, a positive electrode configured to apply a positive electrode voltage to a positive electrode disposed in the electrodeposition tank, a negative electrode configured to apply a negative electrode voltage to the coating object transferred by a hanger, and an electrodeposition controller configured to electrochemically deposit the coating film on an external surface and an internal surface of the coating object by applying the positive electrode voltage to the positive electrode and the negative electrode voltage to the negative electrode, where the electrodeposition controller may be configured to control voltage, current, and pulse in multi-stages over time from a dip-in time point to a draw-out time point of the coating object into and from the electrodeposition tank.

The electrodeposition controller may be configured to adjust the voltage, current, and pulse over time in three stages.

The electrodeposition controller may be configured to set a limit value of an applied voltage such that the applied voltage does not exceed the limit value.

The electrodeposition controller may be configured to increase a current density through a pulse control of the current to increase a throwpower for coating film thickness formation of the internal surface.

The electrodeposition controller may include, a first stage rectifier, a second stage rectifier, and a third stage rectifier for controlling multi-stages of voltage, current, and pulse, and a controller configured to control the voltage, current, and pulse over time through a control program.

The controller may be configured to identify a position of the coating object through on/off signals of a first limit switch and a second limit switch, and selectively control a corresponding rectifier.

The control program may include a display including a charge amount display portion configured to display a total charge amount over time during electrodeposition, a voltage display portion configured to display the voltage over time, a current display portion configured to display the current over time, and a user interface configured to display a control condition setting screen for setting the current, voltage, pulse, and duty ratio according to the time.

The controller may be configured to differently set the current, voltage, pulse, and duty ratio through the user interface depending on the coating object.

The controller may be configured to control the pulse of the current in a range of 5 kHz to 10 kHz.

The controller may be configured to set a duty ratio of the pulse to above 50%.

A method is for controlling electrodeposition coating for electrochemically form a coating film on a coating object dipped in an electrodeposition tank storing an electrodeposition solution, and the method includes, recognizing the coating object entering an electrodeposition area and setting a preset voltage, current, and pulse in a multi-stage control condition depending on the coating object, performing a first stage control while a first limit switch is turned on by dipping in of the coating object into the electrodeposition tank, performing a second stage control with an increased voltage and current compared to the first stage control when a second limit switch is turned on due to movement of the coating object, and performing a third stage control with a further increased voltage and current after finishing the second stage control, at a time when a preset period has lapsed since the second stage control is initiated or at a time when a third limit switch is turned on due to movement of the coating object.

In the performing the third stage control, the voltage may be limited not to exceed a preset limit value.

The performing the third stage control may include increasing a current density through a pulse control of the current to increase a throwpower for coating film thickness formation of the internal surface.

The performing the third stage control may include controlling the pulse of the current in a range of 5 kHz to 10 kHz.

The performing the third stage control may include setting a duty ratio of the pulse to be above 50%.

A pause period may be interposed after the performing the second stage control and before the performing the third stage control.

The exemplary method may further include, after the performing the third stage control, limiting the voltage under a limit value while controlling the current to be unlimited.

According to an exemplary embodiment, during the electrodeposition coating work, the voltage, the current, and the pulse are integrally controlled in multi-stages, and thereby the coating film thickness deviation between the external plate and internal plate of the coating object may be reduced.

In addition, by limiting the voltage under the limit value to reduce the effect of the film resistance and by additionally controlling the pulses to increase current density reaching the internal plate, the throwpower may be improved to reduce the coating film thickness deviation between the external plate and the internal plate.

In addition, by applying a pause period during the electrodeposition coating work, the current pulse power during the control of the last third stage rectifier is increased, and thereby the throwpower is further improved.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an experiment device for analyzing effects of voltage, current, and pulse on electrodeposition coating according to an exemplary embodiment.

FIG. 2 illustrates graphs showing the influence on the coating film thickness by factors in the analysis in FIG. 1.

FIG. 3 schematically shows the system for controlling electrodeposition coating according to an exemplary embodiment.

FIG. 4 shows a 3-stage waveform controlling the current according to an exemplary embodiment.

FIG. 5 schematically illustrates the mechanism of the electrodeposition process according to an exemplary embodiment.

FIG. 6 shows shapes of the current pulse and power according to an exemplary embodiment.

FIG. 7 shows the configuration of the control program of the electrodeposition controller according to an exemplary embodiment.

FIG. 8 shows the result of measuring current density change through an experiment according to an exemplary embodiment.

FIG. 9 is a flowchart schematically showing a method for controlling electrodeposition coating according to an exemplary embodiment.

FIG. 10 shows a scheme for the conventional electrodeposition.

DETAILED DESCRIPTION

In the following detailed description, only certain exemplary embodiments of the present disclosure have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

In addition, unless explicitly described to the contrary, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. In addition, the terms “-er”, “-or”, and “module” described in the specification mean units for processing at least one function and operation, and can be implemented by hardware components or software components, and combinations thereof.

Throughout the specification, terms such as first, second, “A”, “B”, “(a)”, “(b)”, and the like will be used only to describe various elements, and are not to be interpreted as limiting these elements. These terms are only for distinguishing the constituent elements from other constituent elements, and nature or order of the constituent elements is not limited by the term.

In this specification, it is to be understood that when one component is referred to as being “connected” or “coupled” to another component, it may be connected or coupled directly to the other component or be connected or coupled to the other component with a further component intervening therebetween. In this specification, it is to be understood that when one component is referred to as being “connected or coupled directly” to another component, it may be connected to or coupled to the other component without another component intervening therebetween.

The terms used herein are used only for the purpose of describing particular exemplary embodiments and are not intended to limit the present disclosure. Singular expressions include plural expressions unless clearly described as different meanings in the context.

It will be further understood that terms “comprise” and “have” used in the present specification specify the presence of stated features, numerals, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, numerals, steps, operations, components, parts, or combinations thereof

Unless otherwise defined herein, all terms including technical or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. Terms such as those defined in a commonly used dictionary should be interpreted as being consistent with the meaning in the context of the related technology, and are not interpreted in an ideal or excessively formal meaning unless explicitly defined in the present specification.

Hereinafter, a system and method for controlling electrodeposition coating according to an exemplary embodiment is described in detail with reference to the drawings.

Prior to the description of the embodiment, the analysis result of effects of each factor of voltage, current, and pulse on electrodeposition film thickness in electrodeposition control through experiment will be described.

FIG. 1 shows an experiment device for analyzing effects of voltage, current, and pulse on electrodeposition coating according to an exemplary embodiment.

FIG. 2 illustrates graphs showing the influence on the coating film thickness by factors in the analysis in FIG. 1.

Referring to FIG. 1 and FIG. 2, a 4-BOX, the coating object 10 for electrodeposition test, is placed in an electrodeposition tank filled with electrodeposition solution, and the positive electrode (+) and negative electrode (−) were connected to perform characteristic analysis according to voltage, current, and pulse control. In the 4-BOX, three sides (front, upper surface, and rear surface) are opened, and eight surfaces from A to H are formed by four panels each having a hole formed in the center. Here, the outermost surface A of the 4-BOX corresponds to the external plate 11 of the coating object 10, and the innermost surface G side corresponds to the internal plate 12.

As a result of analyzing the effect of the voltage, the current, and the pulse on the electrodeposition film thickness based on this 4-box, there is a characteristic that the higher the voltage, the thicker the electrodeposition film thickness (hereinafter, also called coating film thickness).

In addition, it has been found that, during the electrodeposition, the current affects the coating film thickness formation, but when limited by film resistance, the current has a great influence on the throwpower for the coating film thickness formation of the internal plate 12. Here, the throwpower may be calculated as a ratio (e.g., %) of the coating film thickness of the internal plate 12 to the external plate 11. For example, when throwpower is improved, the coating film thickness deviation of the external plate 11 and the internal plate 12 decreases, and in the opposite case, the deviation increases.

In addition, it has been found that the pulse also affects the throwpower depending on pulse ranges. Specifically, it has been found that, in a specific frequency (for example, 5 kHz-10 kHz) range, the coating film thickness on the surface A (i.e., external plate) decreases, and the coating film thickness on the surface G (i.e., internal plate) increases.

Thus, in a system and method for controlling electrodeposition coating according to an embodiment, voltage, current, and pulse conditions are controlled in multi-stages in order to reduce the coating film thickness difference between the internal plate and the external plate.

FIG. 3 schematically shows the system for controlling electrodeposition coating according to an exemplary embodiment.

Referring to FIG. 3, a system 100 for controlling electrodeposition coating according to an exemplary embodiment includes an electrodeposition tank 110, a positive electrode 120, a negative electrode 130, and an electrodeposition controller 140. The system 100 may further include a transfer rail 160 and a hanger 150 for transferring the coating object 10, as typical devices used in the vehicle electrodeposition process.

In the electrodeposition process, the coating object 10 is dipped into the electrodeposition tank 110 filled with an electrodeposition solution 111, and an electrodeposition film is formed on the surface of the coating object 10 through electrophoresis and electrolysis.

The coating object 10 may be a vehicle body assembled in a vehicle production factory or a component part thereof, and the surface on which the coating film is formed may be divided into the external plate 11 configured on the outside and the internal plate 12 configured on the inside. In the following description, the terms “external plate” and “internal plate” do not necessarily limit that they are independent plates. That is, the outside of a concave recess in a curved plate may be referred to as the external plate, and the inside may be referred to as the internal plate. In other words, “external plate” may refer to the exterior surface of one panel, and “internal plate” may refer to the interior surface of the one panel.

The electrodeposition tank 110 is formed in the form of a water tank, and filled with the electrodeposition solution 111. The electrodeposition solution 111 may include a highly permeable paint to help the coating film formation and to lower coating film thickness of the coating object 10.

The positive electrode 120 includes a positive electrode plate disposed along the inner length direction of the electrodeposition tank 110, and electrically connects a positive electrode voltage (+) of the rectifier 141 to the electrodeposition solution 111.

The negative electrode 130 contacts the surface of the coating object 10 through the hanger 150 and supplied with a negative electrode voltage (−).

The positive electrode 120 and the negative electrode 130 are electrically interconnected through the electrodeposition solution 111 when the coating object 10 is put into the electrodeposition tank 110.

The electrodeposition controller 140 supplies the DC electricity needed to perform the electrodeposition process through at least one rectifier 141. By applying a positive electrode voltage (+) to the positive electrode 120 and a negative electrode voltage (−) to the negative electrode 130, a coating film is electrically deposited on the surface of the coating object.

The electrodeposition controller 140 includes the rectifier 141 capable of voltage, current, and pulse control and a controller 142 for the control.

The rectifier 141 generates the voltage, the current, and the pulse applied to the positive electrode 120 and the negative electrode 130 during electrodeposition process, in response to a control command from the controller 142.

The controller 142 includes a processor, a control program, a control circuit, and data for the overall operation of the system for controlling electrodeposition coating according to an exemplary embodiment. The controller 142 may be configured as a separate information communication device, such as a computer, in conjunction with the rectifier 141, or may be configured as an integrated system integrally mounted on the rectifier 141.

Meanwhile, during the electrodeposition work, in order to minimize the coating film thickness difference of the external plate 11 and the internal plate 12 of the coating object 10, the electrodeposition controller 140 controls the condition for the voltage, current, and pulse control according to time from a dip-in time point of the coating object 10 to a draw-out time point to increase multi-stage. The electrodeposition coating controller 140 controls the current condition according to time from the time point of drawing in to the point of drawing out of the object 10 in multiple stages.

For example, the electrodeposition controller 140 may adjust the voltage, current, and pulse to increase with time in three stages. The electrodeposition controller 140 may include a first stage rectifier 141-1, a second stage rectifier 141-2, and a third stage rectifier 141-3 for preset control of the voltage, current, and pulse, for each stage.

However, an exemplary embodiment is not limited thereto, and the electrodeposition controller 140 may be configured to convert a preset control condition into a multi-stage through one rectifier 141.

In addition, the electrodeposition controller 140 includes a first limit switch SW1 and a second limit switch SW2, which are disposed in each stage area to detect dipping-in and drawing-out of the coating object 10. The limit switches SW1 and SW2 may transfer an on/off signal to the electrodeposition controller 140 depending on whether the hanger 150 that transfers the coating object 10 is touched. It may be understood that the limit switches SW1 and SW2 are not limited to touch sensors described above, and may be implemented as gate sensors to detect entering and exiting of the coating object 10 into and from a corresponding stage area.

Meanwhile, FIG. 4 shows a 3-stage waveform controlling the current according to an exemplary embodiment.

Referring to FIG. 4, the electrodeposition controller 140 controls the current, pulse, and duty ratio of the rectifier 141 in three stages over time. For example, the controller 142 may control the current for each stage to 150 mA for the first stage, 240 mA for second stage, and unlimited to the third stage.

Although the current is not limited in the third stage, the electrodeposition controller 140 may set a limit value for the voltage, and this effectively limit the applicable current, of which the specific value may depend on configuration of the system, since the voltage will be increased in order to apply higher current.

Referring back to FIG. 3, the electrodeposition controller 140 may identify the position of the coating object 10 through on/off signals of the first limit switch SW1 and the second limit switch SW2, and selectively control a corresponding rectifier. At this time, the electrodeposition controller 140 controls the first stage rectifier control condition according to the first limit switch SW1 touch, and controls the second stage rectifier control condition according to the second limit switch SW2 touch. At this time, the electrodeposition controller 140 controls the first stage rectifier 141-1 when the first limit switch SW1 is turned on, and controls the second stage rectifier 141-2 when the second limit switch SW2 is turned on. In addition, the electrodeposition controller 140 starts measuring time elapsed from the turning-on time point of the second limit switch SW2, and when the elapsed time reaches a preset time, the electrodeposition controller 140 switches from the current second stage rectifier control to the third stage rectifier control.

In addition, a third limit switch SW3 may be further configured such that the third stage rectifier 141-3 is used by the electrodeposition controller 140 when the third limit switch SW3 is turned on, thereby achieving a total of 3 stages.

Meanwhile, FIG. 5 schematically illustrates the mechanism of the electrodeposition process according to an exemplary embodiment.

Referring to FIG. 5, firstly as illustrated in the upper left diagram, the electrolysis is caused through DC current applied to the positive electrode 120 and the negative electrode 130 while the coating object 10 is put in the electrodeposition tank 110. Then, as illustrated in the upper right diagram, ionized particles flow to the coating object under the electric field, to form electrode deposition film on the surface of the coating object 10 applied with the negative electrode voltage (-).

During this electrodeposition, when the voltage is simply maintained to a preset voltage, throwpower may be high and the coating film thickness on the external surface may be substantially higher than that on the internal surface.

In addition, when the electrodeposition film is formed on the surface of the coating object 10, the electricity permeates into the electrodeposition film to remove moisture from the electrodeposition film. In this case, when moisture is removed from the electrodeposition film, the electrodeposition film forms electrical resistance.

Therefore, the electrodeposition speed on the external surface is slowed and the electrodeposition may occur on the internal surface relatively faster, as illustrated in the lower right diagram.

Thus, in the conventional scheme, a required coating film thickness on the internal surface may be obtained by simply maintaining applying the voltage. However, in this case, the coating film thickness difference between the external and internal surfaces remains high.

In contrast, in an exemplary embodiment that operates the voltage, current, and pulse are operated in three stages, in addition to the first stage described above, the second stage and third stage are operated to accelerate the deposition on the internal surface thereby reducing the coating film thickness difference between the external and internal surfaces, of which the principle is described below in detail.

Considering the relationship between the electrodeposition film and the current density during the electrodeposition process, increasing the current density may result in a higher form of the electrodeposition film.

In consideration of this, the electrodeposition controller 140 may control the electrodeposition film generation speed by adjusting the current intensity according to time to a multi-stage (e.g., three stages), and may adjust the thickness of the electrodeposition film.

The relationship between electrodeposition film thickness formation and current density may be expressed by Equation 1 below.

$\begin{matrix} {{\Delta S_{D}} = {{\frac{1}{\overset{¨}{A}} \cdot \left( {j_{t} - j_{d}} \right) \cdot \Delta}\; t}} & {{Equation}\mspace{14mu} 1} \end{matrix}$

Here, ΔS_(D) indicates a coating film thickness, j_(t) indicates a current density (A/cm²) at time t, j_(d) indicates a lowest current density (A cm²), Ä indicates an electrochemical equilibrium value (A·S/cm²), and t indicates time.

As shown in Equation 2 below, when the current density j_(t) is lower than the lower limit current density ja due to the film resistance formed high over time, coating film is formed no more.

$\begin{matrix} {\frac{\Delta S_{D}}{\Delta t} = 0} & {{Equation}\mspace{14mu} 2} \end{matrix}$

Here, j_(t)<j_(d).

The current density jt may be expressed as Equation 3 below using Ohm's law.

j _(t)=(k·E)_(t)   Equation 3

Here, E indicates an electric field strength (V/cm), and k indicates an electrical conductivity (S/cm).

In addition, the correlation between the current and the surface area may be expressed by the Equation 4 below.

$\begin{matrix} {{{I = {I_{0} \cdot e^{({{- \frac{a \cdot V}{p \cdot l}} \cdot t})}}},{where}}{a = {{- \frac{dA}{dQ}}\left( {c{{m^{2}/A} \cdot S}} \right)}}} & {{Equation}\mspace{14mu} 4} \end{matrix}$

Here, dA indicates a indicates a surface area that is not panted, dQ indicates a charge amount, V indicates a voltage, p indicates a coating film resistance, I indicates a distance from the coating object to the electrode, and t indicates time.

In this background, the electrodeposition controller 140 according to an exemplary embodiment controls the electrodeposition by utilizing the voltage and current, in comparison with the conventional method utilizing only the voltage. In addition, by increasing the current density reaching the internal plate 12 through additional pulse control, throwpower may be further improved, and the coating film deviation between the external plate 11 and the internal plate 12 may be decreased to be less than 4.

FIG. 6 shows shapes of the current pulse and power according to an exemplary embodiment.

Referring to FIG. 6, when applying the pulses, the electrodeposition controller 140 may improve the throwpower by increasing pulse power of the current per unit time.

At this time, the basic principle of pulse control may be expressed as Equation 5 below. That is, pulse control is to implement pulse control with the same duty ratio as in Equation 5.

$\begin{matrix} {{{Duty}\mspace{14mu}{{cycle}(\%)}} = {\frac{t_{on}}{t_{on} + t_{off}} \times 100(\%)}} & {{Equation}\mspace{14mu} 5} \end{matrix}$

Here, t_(on) indicates a current-on duration, and t_(off) indicates a current-off duration. Here, an average current density i_(a) may be expressed as

${i_{a} = {\frac{t_{on}}{t_{cycle}} \times i_{p}}},$

and here, i_(p) indicates a maximum current density.

For example, the electrodeposition controller 140 may control in the following manners (1) to (4) to increase the entire current density during pulse control.

(1) The nucleation rate I of the coating layer may be expressed as Equation 6 below, where the nucleation rate depends on the negative electrode overvoltage η.

I=t _(on)·exp(−k ₂/η²)   Equation 6

Here, k1 and k2 are constants, and η indicates an overvoltage.

(2) The negative electrode overvoltage η_(DC) of DC current deposition during electrodeposition may be expressed as Equation 7 below.

$\begin{matrix} {\eta_{DC} = {\eta_{0} \cdot {\ln\left( \frac{i_{DC}}{i_{0}} \right)}}} & {{Equation}\mspace{14mu} 7} \end{matrix}$

Here, i_(DC) indicates a DC current, and η₀ and i₀ are constants, where the negative electrode overvoltage η_(DC) becomes η₀ when the DC current i_(DC) equals to i₀.

(3) The overvoltage η_(PC) during pulse deposition may be expressed as Equation 8

$\begin{matrix} {\eta_{PC} = {{\eta_{0} \cdot {\ln\left( \frac{i_{a}}{i_{0}} \right)}} + {\eta_{0} \cdot {\ln\left( {p + 1} \right)}}}} & {{Equation}\mspace{14mu} 8} \end{matrix}$

Here, p=t_(off)/t_(on).

(4) Equation 7 above may be expressed as Equation 9 below because it may be equally applied to the pulse coating method, and the current density may be increased by applying this to the pulse coating method.

i_(DC)=i_(a)

i_(PC)>i_(a)

η_(PC)=η₀+η₀·ln(p+1)

Here, p=t_(off)/t_(on).

FIG. 7 shows the configuration of the control program of the electrodeposition controller according to an exemplary embodiment.

Referring to FIG. 7, a control program according to an exemplary embodiment includes a charge amount display portion 142 a, a voltage display portion 142 b, a current display portion 142 c, and a user interface (UI) 142 d.

Although the FIG. 7 illustrates the control program as sections in displayed in a screen, it may be understood that the control program includes corresponding subroutine or a set of instructions corresponding to the displayed sections.

The charge amount display portion 142 a displays the total charge amount over time during electrodeposition on the monitoring screen.

The voltage display portion 142 b displays the output voltage over time on the monitoring screen.

The current display portion 142 c displays the output current over time on the monitoring screen.

The UI 142 d displays a control condition setting screen for setting current, voltage, pulse, and duty ratio control of the rectifier 141 according to the time.

The controller 142 may set the current in multi-stage, for example, in at least three stages, through the UI 142 d . When the current level is changed according to this current setting, a large current density change is detected not only in the external plate 11 but also in the internal plate 12.

Here, in the controller 142, the coating object 10 may be a variety of materials and component parts, and an optimal condition for each corresponding object 10 may be set according to vehicle body ID (for example, VIN). In addition, the ID of the coating object 10 that enters the electrodeposition process later may be recognized by barcode scan, etc., and the electrodeposition work may be controlled based on the corresponding control condition preset through this process.

Meanwhile, FIG. 8 shows the result of measuring current density change through an experiment according to an exemplary embodiment.

Referring to FIG. 8, the experiment apparatus of FIG. 2 shows the current density measurement result for the 1-st to 4-th panels of the 4-BOX, where the 1-st panel corresponds to the external plate 11 and the 4-th panel is positioned innermost corresponds to the internal plate 12.

When the controller 142 changes the current level, the current density change appears on all panels, and particularly, it is found that a large current density change occurs to the internal plate 12 of the 4-th panel positioned at the innermost position.

Referring back to FIG. 7, the controller 142 sets a limit value for the applied voltage to prevent the applied voltage from exceeding the limit value while the current is controlled in multi-stages, e.g., in three stages, to control. For example, in the case that the limit voltage is set to 220 V, the applied voltage will not exceed the limit value of 220 while the applied voltage increases as the applied current increases. When the voltage exceeds the limit value, it may adversely affect the throwpower of the applied current.

In addition, the controller 142 also sets the pulse control condition when setting the current control condition and may use a range between 5 kHz-10 kHz. At this time, the controller 142 may set the duty ratio (i.e., duty cycle) of the pulse to 50% or more, and may set the value of the current pulse power acting on the unit time to be as large as possible.

In addition, as shown in the monitoring screens of the voltage display portion 142 b and the current display portion 142 c of the FIG. 7, the controller 142 may maximize the pulse effect by putting a pause period for a while (for example, more than 3 seconds), after controlling the current and voltage to the second stage. Due to the pause period, when the current density changes, effective current density change may reach the internal plate 12.

Hereinafter, a method for controlling electrodeposition coating according to an exemplary embodiment based on the system 100 for controlling electrodeposition coating is described with reference to FIG. 9.

FIG. 9 is a flowchart schematically showing a method for controlling electrodeposition coating according to an exemplary embodiment.

Referring to FIG. 9, at step S10, the electrodeposition controller 140 recognizes identification information (ID, for example, VIN) of the coating object 10 entering the electrodeposition process by the hanger 150, and sets multi-stage control condition preset corresponding to the ID.

At step S20, the electrodeposition controller 140 determines whether the first limit switch SW1 is turned on.

When the first limit switch SW1 is turned on by the dip-in of the coating object 10 into the electrodeposition tank 110 (S20—Yes), at step S30, the electrodeposition controller 140 initiates a first stage control of the multi-stage control condition, for example, by using the first stage rectifier 141-1. At this time, the electrodeposition controller 140 may gradually increase the voltage and the current by the first stage control, to prevent a dipping mark due to abrupt application of a high current and voltage.

At step S40, the electrodeposition controller 140 determines whether the second limit switch SW2 is turned on.

When the second limit switch SW2 is turned on due to movement of the coating object 10 (S40—Yes), at step S50, the electrodeposition controller 140 performs a second stage control, for example, by using the second stage rectifier 141-2 after finishing the first stage control. At this time, the electrodeposition controller 140 performs the second stage control with an increased voltage and current compared to the first rectifier control.

In more detail, the electrodeposition controller 140 may control the second rectifier to output the second stage current higher than the first stage current as shown in FIG. 4. The applied current may be controlled higher by controlling the applied voltage higher.

At step S60, the electrodeposition controller 140 determines whether a third stage control shall be initiated. Specifically, FIG. 9 illustrates that the electrodeposition controller 140 determines whether a preset period has elapsed since the second stage control

As an alternative, at the step S60, the electrodeposition controller 140 may determine whether the third limit switch SW3 is turned on. That is, the third stage control may be initiated at a time when the preset period has lapsed since the second stage control is initiated, or at a time when the third limit switch SW3 is turned on due to movement of the coating object 10.

When the preset period has lapsed since the second stage control is initiated or when the third limit switch SW3 is turned on due to movement of the coating object (S60—Yes), the electrodeposition controller 140 finishes the second stage control and initiates a third stage control, at step S70.

At this time, at step S80, the electrodeposition controller 140 performs the third stage control with a further voltage and current compared to the second stage control. In the third stage control, the electrodeposition controller 140 controls the pulse of the current to be in the range of 5 kHz to 10 kHz to increase throwpower by increasing the current density. In addition, the electrodeposition controller 140 may set the duty ratio of the pulse to be above 50%, to increase the pulse power of the current per unit time.

In addition, before initiating the third stage control after finishing the second rectifier control, a pause period (for example, more than 3 seconds) may be interposed, such that the effect of pulse controlling on the current density may be enhance.

In addition, in the third stage control, at step S90, the electrodeposition controller 140 may set the limit value for the voltage to prevent the voltage from exceeding the limit value while controlling the current to be unlimited. As described in connection with the system 100, such limit value may practically limit the current value, which may be depend on the system.

At the step S20, the step S40, and the step S60, when the corresponding criteria is not satisfied, the electrodeposition controller 140 may wait until the corresponding criteria not satisfied.

Thereafter, when the coating object 10 is drawn out of the electrodeposition tank 110, which may be detected by turning off of the third limiter switch SW3, the electrodeposition controller 140 finishes the electrodeposition work of the coating object 10.

As such, according to an exemplary embodiment, during the electrodeposition coating work, the voltage, the current, and the pulse are integrally controlled in multi-stages, and thereby the coating film thickness deviation between the external plate and internal plate of the coating object may be reduced.

Particularly, by limiting the voltage under the limit value to reduce the effect of the film resistance and by additionally controlling the pulses to increase current density reaching the internal plate, the throwpower may be improved to reduce the coating film thickness deviation between the external plate and the internal plate.

In addition, by applying a pause period during the electrodeposition coating work, the current pulse power during the control of the last third stage rectifier is increased, and thereby the throwpower is further improved.

The exemplary embodiments of the present disclosure described above are not only implemented by the apparatus and the method, but may be implemented by a program for realizing functions corresponding to the configuration of the embodiments of the present disclosure or a recording medium on which the program is recorded.

While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. A system for controlling electrodeposition coating for electrochemically forming a coating film on a coating object in an electrodeposition tank storing electrodeposition solution, the system comprising: a positive electrode configured to apply a positive electrode voltage to a positive electrode disposed in the electrodeposition tank; a negative electrode configured to apply a negative electrode voltage to the coating object transferred by a hanger; and an electrodeposition controller configured to electrochemically deposit the coating film on an external surface and an internal surface of the coating object by applying the positive electrode voltage to the positive electrode and the negative electrode voltage to the negative electrode; wherein the electrodeposition controller is configured to control voltage, current, and pulse in multi-stages over time from a dip-in time point to a draw-out time point of the coating object into and from the electrodeposition tank.
 2. The system of claim 1, wherein the electrodeposition controller is configured to adjust the voltage, current, and pulse over time in three stages.
 3. The system of claim 2, wherein the electrodeposition controller is configured to set a limit value of an applied voltage such that the applied voltage does not exceed the limit value.
 4. The system of claim 1, wherein the electrodeposition controller is configured to increase a current density through a pulse control of the current to increase a throwpower for coating film thickness formation of the internal surface.
 5. The system of claim 4, wherein the electrodeposition controller comprises: a first stage rectifier, a second stage rectifier, and a third stage rectifier for controlling multi-stages of voltage, current, and pulse; and a controller configured to control the voltage, current, and pulse over time through a control program.
 6. The system of claim 5, wherein the controller is configured to identify a position of the coating object through on/off signals of a first limit switch and a second limit switch, and selectively control a corresponding rectifier.
 7. The system of claim 5, wherein the control program comprises a display comprising: a charge amount display portion configured to display a total charge amount over time during electrodeposition; a voltage display portion configured to display the voltage over time; a current display portion configured to display the current over time; and a user interface configured to display a control condition setting screen for setting the current, voltage, pulse, and duty ratio according to the time.
 8. The system of claim 7, wherein the controller is configured to differently set the current, voltage, pulse, and duty ratio through the user interface depending on the coating object.
 9. The system of claim 7, wherein the controller is configured to control the pulse of the current in a range of 5 kHz to 10 kHz.
 10. The system of claim 9, wherein the controller is configured to set a duty ratio of the pulse to above 50%
 11. A method for controlling electrodeposition coating for electrochemically form a coating film on a coating object dipped in an electrodeposition tank storing an electrodeposition solution, the method comprising: recognizing the coating object entering an electrodeposition area and setting a preset voltage, current, and pulse in a multi-stage control condition depending on the coating object; performing a first stage control while a first limit switch is turned on by dipping in of the coating object into the electrodeposition tank; performing a second stage control with an increased voltage and current compared to the first stage control when a second limit switch is turned on due to movement of the coating object; and performing a third stage control with a further increased voltage and current after finishing the second stage control, at a time when a preset period has lapsed since the second stage control is initiated or at a time when a third limit switch is turned on due to movement of the coating object.
 12. The method of claim 11, wherein, in the performing the third stage control, the voltage is limited to not exceed a preset limit value.
 13. The method of claim 11, wherein the performing the third stage control comprises increasing a current density through a pulse control of the current to increase a throwpower for coating film thickness formation of the internal surface.
 14. The method of claim 13, wherein the performing the third stage control comprises controlling the pulse of the current in a range of 5 kHz to 10 kHz.
 15. The method of claim 14, wherein the performing the third stage control comprises setting a duty ratio of the pulse to be above 50%.
 16. The method of claim 11, wherein a pause period is interposed after the performing the second stage control and before the performing the third stage control.
 17. The method of claim 11, further comprising, after the performing the third stage control, limiting the voltage under a limit value while controlling the current to be unlimited. 